Intraoperative mapping of expressive language cortex using passive real-time electrocorticography

Abstract

In this case report, we investigated the utility and practicality of passive intraoperative functional mapping of expressive language cortex using high-resolution electrocorticography (ECoG). The patient presented here experienced new-onset seizures caused by a medium-grade tumor in very close proximity to expressive language regions. In preparation of tumor resection, the patient underwent multiple functional language mapping procedures. We examined the relationship of results obtained with intraoperative high-resolution ECoG, extraoperative ECoG utilizing a conventional subdural grid, extraoperative electrical cortical stimulation (ECS) mapping, and functional magnetic resonance imaging (fMRI). Our results demonstrate that intraoperative mapping using high-resolution ECoG is feasible and, within minutes, produces results that are qualitatively concordant to those achieved by extraoperative mapping modalities. They also suggest that functional language mapping of expressive language areas with ECoG may prove useful in many intraoperative conditions given its time efficiency and safety. Finally, they demonstrate that integration of results from multiple functional mapping techniques, both intraoperative and extraoperative, may serve to improve the confidence in or precision of functional localization when pathology encroaches upon eloquent language cortex.

Keywords: Electrical cortical stimulation; Electrocorticography; High-density grid; Intraoperative; Language mapping; fMRI.

Supp. Fig. 1

Functional MRI activity plotted with a threshold of t(150) > 3.91, p_uncorrected < 0.0001.

Fig. 1

(Left) Preoperative axial T2-weighted FLAIR MR image on 1.5 T magnet demonstrating a tumor in the anterior left frontal lobe. (Right) Preoperative fMRI on 3 T magnet indicating proximity of tumor to Broca's area, within 3–5 mm on postprocessed images.

Fig. 2

(A) Intraoperative photograph of left frontal lobe exposure with standard 64-contact subdural grid. (B) Example of subdural grid used during the case, courtesy of PMT Corporation. (C) Intraoperative photograph of high-density grid placed over eloquent cortex previously identified by the standard grid. (D) High-density 64-contact silicon grid used during the case.

Fig. 3

Numbers represent electrode contacts of the standard subdural grid coverage. The tumor margins are displayed as light blue. Electrical stimulation of contacts 11 and 12 (dark blue) caused speech arrest in Broca's area. Electrical stimulation of contacts 23 and 41 (red) caused an electrographic seizure; contacts 1, 2 and 9 (light gray) were removed for better contour along the cortical surface.

Fig. 4

(Top left) Functional MRI showing increased BOLD activity (shown in yellow and orange) in Broca's area, as well as auditory/Wernicke's area, precentral gyrus, supplementary motor/premotor cortex and prefrontal cortex. ECS (white circles) caused speech arrest in Broca's area, adjacent to increased BOLD activity. (Top right) Small black dots represent electrode contacts of the standard extraoperative subdural grid. Results from extraoperative ECoG-based functional mapping (shown in green) demonstrated increased activity in Broca's area, precentral gyrus, supplementary motor/premotor cortex and postcentral gyrus. (Bottom) Results from intraoperative ECoG-based mapping are shown in red. The diameter of each circle is proportional to the activity under the corresponding electrode contact. The largest circles identify locations that are qualitatively concordant with those from extraoperative ECoG-based and ECS mapping.